Florian Westphal <fw@xxxxxxxxx> wrote:
> Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
> > > The confirmed bit should always be set here.
> >
> > So why are you testing it ?
>
> To detect ct object recycling when tuple is identical.
>
> This is my understanding of how we can end up with two
> cpus thinking they have exclusive ownership of the same ct:
>
> A cpu0: starts lookup: find ct for tuple t
> B cpu1: starts lookup: find ct for tuple t
> C cpu0: finds ct c for tuple t, no refcnt taken yet
> cpu1: finds ct c for tuple t, no refcnt taken yet
> cpu2: destroys ct c, removes from hash table, calls ->destroy function
> D cpu0: tries to increment refcnt; fails since its 0: lookup ends
> E cpu0: allocates a new ct object since no acceptable ct was found for t
> F cpu0: allocator gives us just-freed ct c
> G cpu0: initialises ct, sets refcnt to 1
> H cpu0: adds extensions, ct object is put on unconfirmed list and
> assigned to skb->nfct
> I cpu0: skb continues through network stack
> J cpu1: tries to increment refcnt, ok
> K cpu1: checks if ct matches requested tuple t: it does
> L cpu0: sets refcnt conntrack tuple, allocates extensions, etc.
^^^^
> cpu1: sets skb->nfct to ct, skb continues through network stack
sorry, for that brain fart This should only say
L cpu1: sets skb->nfct to ct, skb continues...
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